Reference signal having variable structure

ABSTRACT

A method for transmitting a data demodulation reference signal (DMRS) in a wireless communication system and a device therefor are disclosed. To this end, a basic DMRS is transmitted via the first OFDM symbol in a data transmission region of a predetermined subframe, and an additional DMRS is transmitted in the predetermined subframe in accordance with a level determined by a transmission environment, wherein the basic DMRS is characterized by being transmitted via the first OFDM symbol in the data transmission region of the predetermined subframe regardless of a transmission link, the structure of the subframe, and the transmission environment.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/926,030, filed on Jul. 10, 2020, which is a continuation of U.S.patent application Ser. No. 16/065,113, filed on Oct. 15, 2018, now U.S.Pat. No. 10,771,212, which is the National Stage filing under 35 U.S.C.371 of International Application No. PCT/KR2017/008081, filed on Jul.27, 2017, which claims the benefit of U.S. Provisional Application Nos.62/371,865, filed on Aug. 8, 2016, and 62/405,254, filed on Oct. 7,2016, the contents of which are all hereby incorporated by referenceherein in their entirety.

TECHNICAL FIELD

Following description relates to a method of transmitting and receivinga reference signal having a structure variable according to a systemstatus in a wireless communication system and an apparatus therefor.

BACKGROUND ART

Recently, standardization for a mobile communication technology isarriving at the study on 5G mobile communication after passing through4G mobile communication technologies such as LTE and LTE-A. In 3GPP, the5G mobile communication is referred to as NR (new radio).

According to current NR system design requirements, it is able to seethat there are considerably divergent requirements. For example, afrequency band used by the NR ranges from 700 MHz to 70 GHz, a systembandwidth ranges from 5 MHz to 1 GHz, moving speed has a range rangingfrom 0 km/h to 500 km/h, and environment for the NR includes indoor,outdoor, a large cell, and the like. In particular, the NR requiressupporting in various situations.

In the various requirements existing situation, the most common designdirection is to design a system in consideration of a poorest situationamong the various situations. This can be identically applied to atransmission of a DMRS (demodulation reference signal) corresponding toa reference signal used for decoding data and/or control information.

DISCLOSURE OF THE INVENTION Technical Problem

However, if a signal is transmitted with a single pattern under theassumption of the extreme circumstances, it is very inefficient in termsof resource efficiency. On the contrary, if an NR DMRS including variouspatterns is designed, it may have a problem that implementationcomplexity increases.

In order to solve the problem, a method of configuring a basic DMRS andan additional DMRS by classifying a DMRS and a method of transmittingand receiving a variable RS using the basic DMRS and the additional DMRSare explained in the following.

And, a method of using an RS for decoding control information to decodedata in a specific situation is explained as well.

Technical Solution

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, accordingto one embodiment, a method of transmitting a data modulation referencesignal (DMRS) in a wireless communication system includes transmitting abasic DMRS via the first OFDM symbol within a data transmission regionof a prescribed subframe, and transmitting an additional DMRS in theprescribed subframe according to a level determined in accordance withtransmission environment. In this case, the basic DMRS can betransmitted via the first OFDM symbol within the data transmissionregion of the prescribed subframe irrespective of a transmission link, asubframe structure, and transmission environment.

The basic DMRS can be transmitted via the first OFDM symbol within acommon data transmission region common to both a case that the datatransmission region of the prescribed subframe starts with a downlinkdata transmission region and a case that the data transmission region ofthe prescribed subframe starts with an uplink data transmission region.

The prescribed subframe transmits a downlink control channel via thefirst OFDM symbol, transmits an uplink control channel via the last OFDMsymbol, and may have a structure transmitting data between a region inwhich the downlink control channel is transmitted and a region in whichthe uplink control channel is transmitted.

The additional DMRS can include a first type DMRS using the whole of REs(resource elements) of a single OFDM symbol and a second type DMRS usinga partial RE in a specific time region.

A transmission count of the first type DMRS is determined in theprescribed subframe according to the level determined in accordance withthe transmission environment and the same number of OFDM symbols mayexist between the first type DMRS as many as the determined transmissioncount and the basic DMRS.

The first type DMRS can be transmitted via an OFDM symbol appearingafter an OFDM symbol in which the basic DMRS is transmitted.

The second type DMRS can be transmitted in a prescribed OFDM symbol withan equal frequency space.

The level determined according to the transmission environment can besignaled by RS density information.

The RS density may increase as Doppler Effect is getting intensified,delay spread is getting worse, and an MCS level is higher.

The method can further include repeatedly transmitting an RS forestimating a channel change in the prescribed subframe.

To further achieve these and other advantages and in accordance with thepurpose of the present invention, according to a different embodiment, adata modulation reference signal (DMRS) transmission device in awireless communication system includes a transceiver configured totransmit a basic DMRS via the first OFDM symbol within a datatransmission region of a prescribed subframe and transmit an additionalDMRS in the prescribed subframe according to a level determined inaccordance with transmission environment, and a processor configured tocontrol the transceiver to transmit the basic DMRS and the additionalDMRS. In this case, the processor controls the transceiver to transmitthe basic DMRS via the first OFDM symbol within the data transmissionregion of the prescribed subframe irrespective of a transmission link, asubframe structure, and transmission environment.

The processor can control the basic DMRS to be transmitted via the firstOFDM symbol within a common data transmission region common to both acase that the data transmission region of the prescribed subframe startswith a downlink data transmission region and a case that the datatransmission region of the prescribed subframe starts with an uplinkdata transmission region.

The prescribed subframe transmits a downlink control channel via thefirst OFDM symbol, transmits an uplink control channel via the last OFDMsymbol, and may have a structure transmitting data between a region inwhich the downlink control channel is transmitted and a region in whichthe uplink control channel is transmitted.

The additional DMRS can include a first type DMRS using the whole of REs(resource elements) of a single OFDM symbol and a second type DMRS usinga partial RE in a specific time region.

The processor can determine a transmission count of the first type DMRSin the prescribed subframe according to the level determined inaccordance with the transmission environment and control the same numberof OFDM symbols to be existed between the first type DMRS as many as thedetermined transmission count and the basic DMRS.

Advantageous Effects

According to the present invention, it is able to transmit a DMRSwithout losing efficiency in a situation in which various requirementsexist.

It will be appreciated by persons skilled in the art that the effectsthat could be achieved with the present disclosure are not limited towhat has been particularly described hereinabove and the above and othereffects that the present disclosure could achieve will be more clearlyunderstood from the following detailed description.

DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating a TDD radio frame structure;

FIG. 2 is a diagram illustrating a subframe structure of an NR systemaccording to one embodiment of the present invention;

FIGS. 3 and 4 are diagrams for explaining a method of transmitting abasic DMRS and an additional DMRS according to one embodiment of thepresent invention;

FIGS. 5 and 6 are diagrams for explaining a method of controlling DMRStransmission density according to one embodiment of the presentinvention;

FIG. 7 is a diagram illustrating a concept of a multi-shot measurementRS according to one embodiment of the present invention;

FIG. 8 is a diagram illustrating a method for control information anddata to share an RS according to one embodiment of the presentinvention;

FIG. 9 is a diagram for explaining a method of spreading a DMRS to the Nnumber of REs using a CDM scheme and a method of transmitting a DMRSusing 8 orthogonal codes according to one embodiment of the presentinvention;

FIG. 10 is a diagram for explaining a method of using FDM and CDM via acombination of the FDM and the CDM according to one embodiment of thepresent invention;

FIG. 11 is a diagram for explaining a method of using FDM and OCC via acombination of the FDM and the OCC according to one embodiment of thepresent invention;

FIG. 12 is a diagram for explaining a method of using FDM and CDM via acombination of the FDM and the CDM according to a different embodimentof the present invention;

FIGS. 13 and 14 are diagrams for explaining a method of using FDM andOCC via a combination of the FDM and the OCC according to a differentembodiment of the present invention;

FIG. 15 is a diagram for explaining a method of using FDM and a methodof configuring a space of 8 REs per AP according to a differentembodiment of the present invention;

FIG. 16 is a diagram illustrating a method of applying FDM and CDMaccording to one embodiment of the present invention;

FIG. 17 is a diagram for explaining a device for performingabovementioned operations.

BEST MODE MODE FOR INVENTION

Reference will now be made in detail to the exemplary embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. The detailed description, which will be given below withreference to the accompanying drawings, is intended to explain exemplaryembodiments of the present invention, rather than to show the onlyembodiments that can be implemented according to the present invention.

The following detailed description includes specific details in order toprovide a thorough understanding of the present invention. However, itwill be apparent to those skilled in the art that the present inventionmay be practiced without such specific details. In some instances, knownstructures and devices are omitted or are shown in block diagram form,focusing on important features of the structures and devices, so as notto obscure the concept of the present invention.

As mentioned in the foregoing description, one embodiment of the presentinvention proposes a method of transmitting a data modulation referencesignal (DMRS) in a wireless communication system. To this end, oneembodiment of the present invention proposes that a basic DMRS istransmitted via a first OFDM symbol within a data transmission region ofa prescribed subframe and an additional DMRS is transmitted in theprescribed subframe according to a level determined according totransmission environment.

In this case, the basic DMRS is transmitted via the first OFDM symbolwithin the data transmission region of the prescribed subframeirrespective of a transmission link, a subframe structure, andtransmission environment. The reason why the basic DMRS is transmittedvia the first OFDM symbol within the data transmission region of theprescribed subframe is to help data early decoding and measure/cancelinter-cell interference.

As mentioned in the foregoing description, the basic DMRS corresponds toa reference signal which is always transmitted irrespective of a link(i.e., DL/UL/SL), numerology (subcarrier spacing, OFDM symbol duration),a transmission layer (rank 1˜N), a deployment scenario (indoor,outdoor), velocity (0˜500 km/h), a TBS size, and the like. In NR, assumethat the basic DMRS is positioned at a forepart of a data region of asubframe. In NR, early decoding of data is an important requirement indesigning the NR system. If a DMRS is transmitted prior to a datasignal, it is able to promptly obtain channel estimation informationwhich is mandatorily required for performing data decoding.

When a position of a basic DMRS is considered, it is also necessary toconsider a subframe structure used in the NR. In the NR system, it isanticipated that a TDD scheme is to be mainly used due to a pilotcontamination problem caused by the introduction of massive MIMO.

FIG. 1 is a diagram illustrating a TDD radio frame structure.

A TDD radio frame shown in FIG. 1 corresponds to a radio frame structureof 4G LTE system. In the following description, unless there is aspecial citation, it may use the radio frame structure.

A TDD radio frame of LTE system has a length of 10 ms and includes 10subframes. In particular, one subframe has a length of 1 ms. In FIG. 1,a special subframe such as a subframe 1 and a subframe 6 corresponds toa subframe for DL/UL switching. A DL pilot time slot (DwPTS) has alength of 3 to 12 OFDM symbols, a guard period (GP) has a length of 1 to10 OFDM symbols, and a UL pilot time slot (UpPTS) has a length of 1 to 2OFDM symbols.

In the 4G LTE radio frame structure shown in FIG. 1, 1 TTI has a lengthof 1 ms and corresponds to one subframe.

FIG. 2 is a diagram illustrating a subframe structure of an NR systemaccording to one embodiment of the present invention.

When communication is performed using a TDD scheme in 5G mobilecommunication system, as shown in FIG. 2, the present invention proposesto use a subframe structure sequentially including a DL-dedicatedsection, a UL/DL variable section, and a UL-dedicated section. By doingso, it is able to prevent a response for a signal transmitted by a linkin one direction from being excessively delayed. If a variable sectionis configured according to a system status, it is able to performflexible communication.

The subframe structure shown in FIG. 2 can be referred to as aself-contained frame structure. In the self-contained frame structure, aDL-dedicated section is used for transmitting DL control channelinformation, a variable section is used for transmitting a data channel,and a UL-dedicated section can be used for transmitting UL controlchannel.

When a position of a basic DMRS is considered, it is also necessary toconsider the following. In NR, a frame structure should be designed tobe commonly used by DL/UL/SL. In order to estimate a channel of aninterference signal received from an adjacent cell or an adjacent link,a DLRS position of DL/UL/SL is matched within a subframe.

FIGS. 3 and 4 are diagrams for explaining a method of transmitting abasic DMRS and an additional DMRS according to one embodiment of thepresent invention.

As shown in FIG. 3 and FIG. 4, in a subframe structure considered in NR,a starting point of a DL data region and a starting point of a UL dataregion may vary according to a length of a DL control region and theexistence of a guard period.

For example, if DL data is transmitted immediately after a first OFDMsymbol in which a control channel is transmitted, a data region maystart from a second OFDM symbol. If UL data is transmitted immediatelyafter a first OFDM symbol in which a control channel is transmitted, asecond OFDM symbol is used as a guard period and a data region may startfrom a third OFDM symbol.

Since a starting point of a DL data region and a starting point of a ULdata region vary, it is preferable to assign a basic DMRS to the firstsymbol among OFDM symbols commonly used for transmitting data in the DLdata region and the UL data region. FIG. 3 illustrates a case that abasic DMRS is transmitted in the third OFDM symbol according to theabovementioned principle.

Meanwhile, an OFDM symbol length of a control region and an OFDM symbollength of a data region may vary. In this case, similar to theabovementioned case, it may assign a basic DMRS to the first OFDM symbolamong OFDM symbols commonly used for transmitting data in the DL dataregion and the UL data region after an OFDM symbol occupied by DLcontrol and guard time. For example, FIG. 4 illustrates a case that bothDL control and guard time are configured in the first OFDM symbol. Inthis case, a basic DMRS can be transmitted in the second OFDM symbol.

An additional DMRS can be positioned at a specific position of a dataregion. The additional DMRS can be classified into two types describedin the following.

(1) Type-1 additional DMRS: A DMRS using a part of an RE (resourceelement).

(2) Type-2 additional DMRS: A DMRS using the whole of an OFDM symbol.

When an additional DMRS is used in a unit of an OFDM symbol (in case ofusing the type-2 additional DMRS), the additional DMRS can be positionedat a location where the number of OFDM symbols appearing after an OFDMsymbol used as a basic DMRS is identical or similar to the number ofOFDM symbols appearing after an OFDM symbol used as an additional DMRS.For example, as shown in FIG. 3, when there are 12 OFDM symbols in adata region and a basic DMRS is positioned at the second OFDM symbol, anadditional DMRS can be assigned to the seventh OFDM symbol. As adifferent example, when there are 12 OFDM symbols in a data region andthere are one basic DMRS and two additional DMRSs, if the basic DMRS andthe additional DMRSs are assigned to the first, the fifth, and the ninthOFDM symbol, respectively, the number of OFDM symbols appearing aftereach DMRS may become similar. By doing so, it may have a merit in that aDMRS is able to reflect a channel estimation change well.

Meanwhile, unlike the aforementioned embodiment, according to adifferent embodiment of the present invention, if an additional DMRS isused in a unit of an OFDM symbol (in case of using the type-2 additionalDMRS), the additional DMRS can be positioned at an OFDM symbolcontiguous with an OFDM symbol used as a basic DMRS. For example, if abasic DMRS is positioned at the second OFDM symbol, an additional DMRScan be assigned to the third OFDM symbol. By doing so, it may have amerit in that the number of resources of DMRS can be increased toincrease the number of antenna ports in multi-antenna transmission orincrease the number of UEs transmitted at the same time.

Additional DMRSs are distinguished from each other by a level accordingto the number of REs of an added DMRS and the number of REs of the addedDMRS (i.e., additional DMRS level) can be controlled according totransmission environment. Among multiple additional DMRS levels, it ispreferable to make one of the multiple additional DMRS levels correspondto a case of transmitting a basic RS only. In particular, an additionalDMRS level 0 may correspond to a case of transmitting a basic RS only.

As shown in FIGS. 3 and 4, an additional DMRS in an RE unit (type-1DMRS) can be arranged with an equal interval. In general, the additionalDMRS in the RE unit defines the number of APs identical to the number ofAPs defined in a basic DMRS. However, when a phase change amount ismeasured between OFDM symbols using the additional DMRS in the RE unitand an amount of change is similar in all APs, it may define additionalDMRSs of the number of APs less than the number of APs defined in thebasic DMRS.

In this case, a basic DMRS can also be referred to as a fundamentalDMRS, a primary DMRS, or the like and an additional DMRS can also bereferred to as a high quality RS, a high performance RS, a supplementalDM-RS, a secondary DM-RS, an add-on DMRS, or the like. And, an RS usablefor decoding data/control information can be referred to as a differentterm rather than a DMRS.

Method of Changing Density of DMRS

In order to change density of a DMRS, it may be able to maintain alegacy RS and add an additional RS according to on-demand. For example,it may add the additional RS in high MCS when Doppler is intensified,delay spread is getting worse, or according to an MCS level.

As a method of changing density of a DMRS, it may have variability thattransmits more RSs or less RS on demand to a user allowing density to bechanged according to capability of a receiving end. For example, if areceiving end is able to perform analog beamforming, it may ask thereceiving end to transmit less RS on demand in response to RStransmission assuming Omni direction reception.

When paging, a random access response, system information, and the likeare transmitted on a channel, density of an RS is fixed on the channel.When information is transmitted to a specific UE on a channel, RSdensity variability can be applied to the channel.

It may be able to define RS density control information from among grantmessages for channel decoding. In particular, information on RS density(use of default density, density increase, density decrease) used in acurrently transmitted channel can be provided in a form described in thefollowing.

Information on RS density (default, density increase/decrease) to beused in a channel

Additional DMRS level information

Information on additional DMRS type

Triggering message for reporting amount of change of channel

When a UE performs short term measurement (CSI-RS), the UE can reportnot only CSI but also an amount of change of a channel (of time andfrequency). The report on the amount of change of a channel may becomean indicator indicating whether to change RS density. And, the UE mayreport an RS density variability request message.

When the UE reports the CSI (RI/PMI/CQI), it may be able to configurethe UE to report information on an additional DMRS level preferred bythe UE. The preferred additional DMRS level corresponds to an additionalDMRS level capable of obtaining the optimized throughput when the UEreceives PDSCH of MCS corresponding to the CQI. When the UE calculatesthe CSI, it may be able to configure the UE to reflect DMRS RE overheadwhich is added according to a level of an additional DMRS.

If a transmission layer increases, it may add an additional RS to alegacy RS.

It is preferable to basically use a basic DMRS and an additional DMRS ina common control channel or a data region indicated by a common controlmessage.

When data is indicated by a UE-specific control channel or a UE-specificcontrol message, DMRS density is variably managed in a subframe. To thisend, it may be able to configure a DMRS-related indicator in a controlmessage. DMRS density is indicated for PDSCH and PUSCH (e.g., DCI,according to a format, RRC).

A UE performing analog Rx beamforming can ask DMRS density to bechanged.

FIGS. 5 and 6 are diagrams for explaining a method of controlling DMRStransmission density according to one embodiment of the presentinvention.

Specifically, FIG. 5 is a diagram for explaining a DMRS transmissionstructure for transmitting DL data and FIG. 6 is a diagram forexplaining a DMRS transmission structure for transmitting DL data.

As shown in FIGS. 5 and 6, a type-2 additional DMRS is classified into alevel 0 and a level 1 according to overhead and the DMRS is usedaccording to a level. In the present example, a DMRS position of a ULtransmission region is matched with a DMRS position of a DL transmissionregion according to a level of the type-2 additional DMRS. Inparticular, a position at which an additional DMRS is transmitted is thesame irrespective of DL/UL data transmission. In particular, it ispreferable to transmit a basic/additional DMRS at the same positionirrespective of DL/UL data transmission.

Since the level 1 increases overhead compared to the level 0, the level1 can be applied for the purpose of enhancing channel estimationperformance, when higher rank transmission or lower rank transmission isperformed. The level 0 is targeting lower rank transmission having lowRS overhead.

As a different example, in FIGS. 5 and 6, A. level 1 (higher rank) isused for the purpose of enhancing channel estimation performance whenlower rank transmission is performed and B. level 1 (lower rank) can beutilized as a pattern for a higher rank.

The structures shown in FIGS. 5 and 6 are an exemplary frame structure.In the present example, a case of using two OFDM symbols in a DL controlregion has been assumed. It is able to transmit DL data in a regionrather than the DL control region bay passing through DL datatransmission time or guard time.

Designating Level Capable of Performing Interpolation to Improve ChannelEstimation Performance

According to one embodiment of the present invention, it may assume aQCL condition for a DMRS transmitted by multi-level. For example, if QCLis assumed among a plurality of DMRSs transmitted in a single subframe,a channel estimated from each of a plurality of the DMRSs can beutilized for interpolation. If QCL condition is assumed in multiplesubframes, it is able to perform interpolation using a multi-subframelevel. When a mini-subframe is defined in a subframe and a DMRS istransmitted according to a mini-subframe, if QCL of a mini-subframelevel is assumed, it may be able to perform interpolation betweenmini-subframes.

A QCL condition may indicate a time domain resource unit capable ofperforming interpolation using such an expression as a subframe group ora multi-subframe group, etc.

Reference Signal Structure for Measuring Channel State Change

Similar to legacy LTE, in case of using a CRS periodically transmittedwith a prescribed OFDM symbol interval or a CSI-RS periodicallytransmitted in a unit of a subframe, it may be able to measuretime-varying characteristic of a channel. On the contrary, in NR, such asingle-beamformed (there is no change of a beam in a unit of time andfrequency) RS as a CRS transmitted in a unit of several OFDM symbols isnot defined.

Since the NR aims for a frame structure capable of dynamically changingDL/UL and a transmission beam in a unit of an OFDM symbol and a unit ofa subframe, it is difficult to transmit a periodic CSI-RS in a unit of asubframe. Hence, it is difficult to use the periodic CSI-RS. And, it isdifficult to perform Doppler measurement using one shot transmission.

Although an RS for measuring a periodically transmitted beam isintroduced, if the RS is not transmitted with a very short period, it isdifficult to measure an amount of change of time-varying characteristicusing the RS for measuring the beam.

Hence, it is necessary to design a channel measurement reference signal(e.g., CSI-RS, SRS, etc.) of the NR to be appropriate for measuring achannel time-varying state change.

A structure of a signal capable of measuring an amount of change of achannel state is described in the following.

FIG. 7 is a diagram illustrating a concept of a multi-shot measurementRS according to one embodiment of the present invention.

A multi-shot CSI-RS or a multi-shot SRS including no beamforming changecan be transmitted as shown in FIG. 7. The multi-shot CSI-RS or themulti-shot SRS can be transmitted over a multi-shot (a multi-shottransmitted in a unit of adjacent subframes or a unit of severalsubframes) in a subframe. It may define a message (e.g., N-subframegroup) on the premise that there is no change in a beamformingcoefficient. And, it may consider a repeatedly transmitted structure ina single OFDM symbol.

When an aperiodic CSI-RS is transmitted, CSI is measured, or CSIreporting is triggered via DCI, a base station indicates whether theCSI-RS corresponds to a single shot CSI-RS or a multi-shot CSI-RS. Ifthe base station transmits the multi-shot CSI-RS, a UE reports a channelchange amount or a preferred additional DMRS level.

When an aperiodic SRS transmission is triggered via DCI, the basestation indicates whether the SRS corresponds to a single shot SRS or amulti-shot SRS. Or, the base station indicates the number ofcontinuously transmitting the SRS with the same precoding scheme.

In addition, in order to efficiently measure interference, a CSI-IM(interference measurement) resource corresponding to a resource forspecifying interference is configured as a multi-shot resource. Themulti-shot CSI-IM resource can be defined in a manner of being matchedwith a CSI-RS resource by one to one. In particular, the base stationcan designate how many times the CSI-RS resource and the CSI-IMresources appear via DCI. On the other hand, the base station may beable to use a scheme of individually designating how many times theCSI-RS resource appears and how many times the CSI-IM resource appearsvia DCI.

Meanwhile, according to a different embodiment of the present invention,as a method of providing a variable RS structure, a method of sharing anRS by a control channel and a data channel is explained.

Method of Sharing RS by Control Channel and Data Channel

As mentioned in the foregoing description, NR system considersperforming TDM on a downlink control channel and a downlink/uplink datachannel. Basically, an RS for demodulating a control channel is definedand a DMRS for demodulating a data channel can be defined, respectively.If an RS is defined for each of channels, RS overhead can beconsiderably increased.

In order to reduce the RS overhead, it may consider methods of sharing acontrol channel RS or a data DMRS in a control channel and a datachannel. However, it is necessary to note that the RS sharing is notalways beneficial in one embodiment of the present invention. Forexample, the control channel RS defines the limited number of antennaports. If the limited number of antenna ports is applied to the datachannel, it may set a limit on the maximum transmission rank of the datachannel. Consequently, the limited number of antenna ports may become anelement that restricts capacity. And, the RS of the control channel maycorrespond to a UE-specific RS or a non-UE-specific RS. If the RS of thecontrol channel is transmitted as a non-UE-specific RS, since it isdifficult to perform beamforming on a specific user, it is difficult toexpect a beam gain.

According to one embodiment of the present invention, the abovementionedRS sharing can be permitted only when a prescribed condition issatisfied. For example,

1. a user transmitting information requiring a non-high data rate,

2. when UE-specific spatial channel information is not obtained or whenobtained spatial channel information is not valid,

3. a user prefers open-loop transmission such as fast movingenvironment,

the abovementioned conditions can be included in the prescribedcondition.

In particular, the present embodiment proposes that a data channelshares an RS defined in a control channel. In this case, it may assumethat the RS of the control channel corresponds to a UE group-specificRS. In this case, as mentioned in the foregoing description, the numberof data transmission layers can be restricted by the RS of the controlchannel. And, it may be difficult to expect UE specific beamforming.

In case of sharing the RS of the control channel, it may not use an RSof a DMRS region. The DMRS region ca ne utilized for transmittingadditional data. As a different embodiment, it may be able to assign anadditional RS to a data region in which the RS of the control channel isshared.

In case of using an additional RS, it may have a merit in that it isable to use a basic transmission (or a fall back scheme) withoutconsiderably increasing RS overhead compared to a single OFDM symbolDMRS. This scheme can be considered as being similar to theaforementioned basic DMRS/additional DMRS scheme.

FIG. 8 is a diagram illustrating a method for control information anddata to share an RS according to one embodiment of the presentinvention.

In FIG. 8, an RB 810 corresponds to an RB performing the aforementionedRS sharing and an RB 820 and an RB 830 correspond to normal RBs notusing the RS sharing.

When a user or a user group shares an RS of a control channel, it ispreferable to additionally transmit an RS similar or identical to the RSof the control channel in a data channel section for the user or theuser group. In particular, FIG. 8 illustrates a case that an RS of apattern identical to the RS of the control channel is transmitted.

The abovementioned structure can operate in a manner of being indicated.To this end, it may define an indicator in contents of a control signal.

Or, when a user or a user group shares an RS of a control channel in adata channel, it is able to configure a control channel RS to be alwaysadditionally transmitted in a data channel section for the UE or the UEgroup.

It is preferable for a base station to indicate an RS to be used to aUE. For example, the base station can indicate an RS defined in acontrol channel or an RS defined in a DMRS region to the UE.

Or, an RS in use can be determined in accordance with an attribute of ashared channel transmitted to a UE. For example, it may be able to sharean RS of a control channel in a data channel indicated by DCI detectedby RNTI. In this case, the RNTI can be associated with RNTI of DCI thattransmits system information or random access response.

Based on the aforementioned description, a transmission structure of anNR DMRS is explained in detail in the following.

According to one embodiment of the present invention, an NR DMRSallocates a resource to make the maximum N (=8) number of antenna ports(APs) to be transmitted in a single OFDM symbol. In this case,multiplexing between APs can be performed using FDM-CDM scheme. In aunit resource block, it may have 2 or 3 REs per AP. It may have themaximum 2N (=16) REs or 3N (=24) REs per RB. The number of effective REsper AP can be differently determined according to the number of layers.

Design Criteria

The maximum spectral efficiency required by NR system is 30 bps/Hz (DL)and 15 bps/Hz (UL). The maximum spectral efficiency is identical tospectral efficiency of 3GPP LTE-A. LTE-A has achieved modulation of64QAM, the number of layers of 8 (DL) and 4 (UL), and requirements of 30bps/Hz (DL) and 15 bps/Hz (UL). Similarly, it is preferable for the NRsystem to achieve the maximum number of layers of 8 (DL) and 4 (UL) inconsideration of spectral efficiency requirement. It is able to increasethe number of antenna ports in accordance with the increase of basestation antennas. Assume that the maximum number of layers capable ofbeing transmitted by the base station corresponds to 16. And, assumethat the maximum number of layers capable of being received by the basestation in UL also corresponds to 16.

Assume the number of point-to-point transmission layers

SU transmission: maximum 8 (DL), maximum 4 (DL)

MU transmission: maximum 4 (DL), maximum 4 (DL)

Assume the maximum number of layers capable of being transmitted by basestation

Maximum 16 (DL), 8 (UL)

In the present design, an NR DMRS is designed under the assumptiondescribed in the following.

Maximum 8 antenna ports are supported according to UE

Maximum 16 antenna ports capable of being transmitted at the same timeare supported

A resource is configured to make the maximum 8 APs to be determined inone OFDM symbol

An antenna port (AP) has at least 2 RE energy or 3 RE energy

If 16 REs are used for 8 APs, 2 REs are used for an AP. If 24 REs areused, 3 REs are used for an AP. In the present design, assume that aresource block is configured by 16 REs or 24 REs corresponding to amultiple of 8.

Method of Performing Multiplexing with Single OFDM Symbol

When a plurality of APs are multiplexed with a single OFDM symbol, itmay use a FDM method using a different frequency resource for an AP anda CDM method separately using a code resource for the same resource.

FIG. 9 is a diagram for explaining a method of spreading a DMRS to the Nnumber of REs using a CDM scheme and a method of transmitting a DMRSusing 8 orthogonal codes according to one embodiment of the presentinvention.

In particular, as an example of using an orthogonal code for the Nnumber of REs, all APs share a scrambling sequence (e.g., a PN sequence,CAZAC, etc.) of a length N and 8 orthogonal sequences (e.g., DFT,Hadamard) each of which has a length N are allocated to an AP.

FIG. 10 is a diagram for explaining a method of using FDM and CDM via acombination of the FDM and the CDM according to one embodiment of thepresent invention.

FIG. 10 also illustrates an example of using a frequency resource and anorthogonal code for the N number of REs. The N number of REs are dividedinto even-numbered REs and odd-numbered REs and an orthogonal code isused to identify 4 APs in each group. A scrambling sequence (e.g., a PNsequence, CAZAC, etc.) of a length N used in an allocated band uses twosubset sequences including an even number index and an odd number indexand each of the subset sequences is shared by an AP. 4 orthogonalsequences (e.g., DFT, Hadamard) each of which has a length N/2 areallocated to an AP.

A scrambling sequence of a length N/2 used in an allocated band isidentically used in two frequency resources and 4 orthogonal sequenceseach of which has a length N/2 are allocated to an AP.

FIG. 11 is a diagram for explaining a method of using FDM and OCC via acombination of the FDM and the OCC according to one embodiment of thepresent invention.

In particular, as an example of using a frequency resource and anorthogonal code for the N number of REs, 4 consecutive frequencyresources are grouped and 4 orthogonal code resources are allocated to 4APs in the group of the frequency resources. Another group of frequencyresources is generated in adjacent 4 REs and 4 orthogonal code resourcesare allocated to another 4 APs. When an RB uses 4 REs, the total N/4numbers of resource groups having 4 consecutive frequencies aregenerated and 4 APs use resource groups away from each other with aspace of 4 REs. A scrambling sequence of a length of N/4 defined in thecorresponding RB is used in each of the N/4 number of frequency groups.

FIG. 12 is a diagram for explaining a method of using FDM and CDM via acombination of the FDM and the CDM according to a different embodimentof the present invention,

The total 4 groups of frequency resources are generated by groupingfrequency resources each of which has a space of 4 REs. In each of the 4groups of frequency resources, 2 APs are distinguished from each otherusing an orthogonal resource.

A scrambling sequence of a length of N defined in a corresponding RB ismapped to each RE and a different scrambling sequence can be mappedbetween groups of frequency resources. It may use OCC-2 ([+1 +1], [+1−1]) as two orthogonal resources.

A scrambling sequence of a length of N/4 defined in a corresponding RBis mapped to an RE belonging to a group of frequency resources andgroups of frequency resources may use the same scrambling sequence as abase sequence. It may introduce a special offset sequence between thegroups. It may use OCC-2 ([+1 +1], [+1 −1]) as two orthogonal resources.

FIGS. 13 and 14 are diagrams for explaining a method of using FDM andOCC via a combination of the FDM and the OCC according to a differentembodiment of the present invention.

Referring to FIG. 13, the total 4 groups of frequency resources aregenerated by grouping frequency resources each of which has a space of 4REs. In each of the 4 groups of frequency resources, 2 APs aredistinguished from each other using an orthogonal resource.

Referring to FIG. 14, two consecutive REs are used as an OCC applicationunit and the total 4 OCC groups are generated 8 REs. A scramblingsequence of a length of N/2 defined in a corresponding RB is mapped toeach of the OCC groups.

FIG. 15 is a diagram for explaining a method of using FDM and a methodof configuring a space of 8 REs per AP according to a differentembodiment of the present invention.

The number of REs per port can be fixed irrespective of the number oflayers (e.g., N-RE/the maximum number of APs). Meanwhile, the number ofREs per port may vary according to the number of layers. (e.g., Singlelayer: 24 REs per port, Two layers: 12 REs per port, Three layers: 8 REsper port, Four layers: 6 REs per port, Six layers: 4 REs per port, Eightlayers: 3 REs per port)

If there are 5 layers, a DMRS pattern for 6 layers uses 5 ports. Ifthere are 7 layers, a DMRS pattern for 8 layers may use 7 ports.

In the foregoing description, a method of allocating a DMRS resource formaximum 8 APs has been explained. However, the method can also be usedas a method of allocating a resource to APs of a smaller range. Forexample, if there are 4 APs, it may use a subset of the method. In caseof extending the number of antenna APs (e.g., maximum 8), it may use onemore OFDM symbol. For example, it is able to identify an AP by applyingOCC-2 to two OFDM symbols. Table 1 in the following assumes LTE-A: 8ports, 24 REs

TABLE 1 Number of AP 1 2 3 4 5 6 7 8 RE/AP 12 6, 6 6, 6, 12 6, 6, 6, 63, 3, 6, 6 3, 3, 3, 3 3, 3, 3, 3 3, 3, 3, 3 3 3 3 3, 3, 3 3, 3, 3, 3

Sequence for CDM

In case of a legacy LTE UL DMRS, a ZC sequence is used as a basesequence and a DFT vector having a space as much as 12 is used(exp(j*2*pi*n*k/12)) to apply time domain cyclic shift. Among 12orthogonal vectors, 8 vectors are used and the vectors are repeatedlyapplied in a unit of 12 REs.

In a new system, when 8 orthogonal DMRS antenna ports (APs) aremultiplexed with one OFDM symbol, it may consider a method of applyingCDM or an OCC in frequency axis.

(1) In case of applying time domain cyclic shift, a DFT vector having aspace as much as 8 (exp(j*2*pi*n*k/8)) is used. This method has a meritin that an impulse response for a radio channel of each of 8 layers isarranged with the maximum space in time domain.

In particular, the method can be applied to a pattern that 8 orthogonalDMRS antenna ports are used by CDM.

As an orthogonal sequence, it may apply Hadamard-8.

In this case, when 12 REs are defined as 1 RB, if a vector of a lengthof 8 is arranged to 12 REs, it may have a form that a vector of 1 cycleis mapped to a part of the vector. For example, when a vector of alength of 8 corresponds to [S_(n)(0) S_(n)(1) S_(n)(2) S_(n)(3) S_(n)(4)S_(n)(5) S_(n)(6) S_(n)(7)], the vector can be mapped to 12 REs in anorder described in the following.

12 RE mapping: [S_(n)(0) S_(n)(1) S_(n)(2) S_(n)(3) S_(n)(4) S_(n)(5)S_(n)(6) S_(n)(7) S_(n)(0) S_(n)(1) S_(n)(2) S_(n)(3)]

In order to make sequences mapped to multiple RBs have a continuousphase, it may be able to configure a mapping relation according to an RBnumber.

TABLE 2 0 1 2 3 4 5 6 7 8 9 10 11 Even (/Odd) number RB [S_(n)(0)S_(n)(1) S_(n)(2) S_(n)(3) S_(n)(4) S_(n)(5) S_(n)(6) S_(n)(7) S_(n)(0)S_(n)(1) S_(n)(2) S_(n)(3)] Odd (/Even) number RB [S_(n)(4) S_(n)(5)S_(n)(6) S_(n)(7) S_(n)(0) S_(n)(1) S_(n)(2) S_(n)(3) S_(n)(4) S_(n)(5)S_(n)(6) S_(n)(7)]

(2) In case of applying time domain cyclic shift, a DFT vector having aspace as much as 4 (exp(j*2*pi*n*k/4)) is used. This method has a meritin that an impulse response for a radio channel of each of 4 layers isarranged with the maximum space in time domain.

In particular, the method can be applied to a pattern that 4 orthogonalDMRS antenna ports are used by CDM.

As an orthogonal sequence, it may apply Hadamard-4.

When an orthogonal DMRS AP is defined using FDM and CDM, if 12 REs aredefined as 1 RB, CDM is applied in a unit of 6 REs to identify 4 DMRSAPs and another 4 DMRS APs can be defined by applying CDM to another 6REs. In this case, if a vector of a length of 4 is arranged to 6 REs,similar to the aforementioned mapping, it may have a form that a vectorof 1 cycle is mapped to the half of the cycle. In this case, asmentioned in the foregoing description, in order to make sequencesmapped to multiple RBs have a continuous phase, it may be able toconfigure a mapping relation according to an RB number.

TABLE 3 0 1 2 3 4 5 6 7 8 9 10 11 Even (/Odd) number RB [S_(n)(0) —S_(n)(1) — S_(n)(2) — S_(n)(3) — S_(n)(0) — S_(n)(1) —] Odd (/Even)number RB [S_(n)(2) — S_(n)(3) — S_(n)(0) — S_(n)(1) — S_(n)(2) —S_(n)(3) —]

Method of Applying FDM and CDM

If 12 REs are defined as 1 RB, CDM is applied in a unit of 6 REs toidentify 4 antenna ports and another 4 antenna ports can be defined byapplying CDM to another 6 REs.

FIG. 16 is a diagram illustrating a method of applying FDM and CDMaccording to one embodiment of the present invention.

Specifically, FIG. 16(A) illustrates a case that 2 consecutive REs aregrouped and groups are arranged with a space of 2 REs. Meanwhile, FIG.16(B) illustrates a case that REs having a space of 2 REs are grouped.

It may be able to identify 4 antenna ports in each of 2 groups (G1, G2).In this case, it may be able to apply the aforementioned CDM code toeach group.

When multi-user transmission is performed in DL transmission, a basestation can allocate a DMRS port within a FDM group and a CDM group toenable multiple users to perform channel estimation. The base stationcan indicate a DMRS port to be used by each user. Basically, the basestation designates a DMRS port used by an individual user. When a DMRSantenna port is assigned to the multiple users, if a UE is aware ofinformation on a DMRS port used by other users, it is highly probable toimprove channel estimation performance.

For example, when two DMRS ports are assigned to a UE and two sequencesare selected from CDM, the UE can identify the two DMRS ports byperforming averaging in a unit of 2 REs. Since it is probable that theremaining two sequences are selected from the CDM for a different UE,the UE performs averaging in a unit of 4 REs to identify two DMRSantenna ports.

It is preferable to perform averaging on REs as close as possible inconsideration of frequency selectivity of a radio channel. Whenaveraging is performed on two REs rather than 4 REs, it may be able toexpect better channel estimation performance. If a base station informsa UE of multi-user multiplexing-related information or information on alength of CDM in multi-user transmission, the UE is able to adjust aunit of performing averaging when the UE estimates a channel. Forexample, it may be able to configure an indicator indicating eitherCDM-2 (use of an orthogonal resource of a length of 2) or CDM-4 (use ofan orthogonal resource of a length of 4) to the UE.

FIG. 17 is a diagram for explaining a device for performingabovementioned operations.

In FIG. 17, a wireless device 800 corresponds to a specific UE in theforegoing description and a wireless device 850 may correspond to a basestation or an eNB.

The UE can include a processor 810, a memory 820, and a transceiver 830and the eNB 850 can include a processor 860, a memory 870, and atransceiver 880. The transceiver 830/880 transmits/receives a radiosignal and can be executed in a physical layer. The processor 810/860 isexecuted in a physical layer and/or a MAC layer and is connected withthe transceiver 830/880. The processor 810/860 can perform a procedureof transmitting the aforementioned SS block.

The processor 810/860 and/or the transceiver 830/880 can include anapplication-specific integrated circuit (ASIC), a different chipset, alogical circuit, and/or a data processor. The memory 820/870 can includea ROM (read-only memory), a RAM (random access memory), a flash memory,a memory card, a storing media and/or a different storing unit. When oneembodiment is executed by software, the aforementioned method can beexecuted by a module (e.g., process, function) performing theaforementioned function. The module can be stored in the memory 820/870and can be executed by the processor 810/860. The memory 820/870 can bedeployed to the inside or outside of the processor 810/860 an can beconnected with the processor 810/860 by a well-known medium.

Preferred embodiments of the present invention have been described indetail above to allow those skilled in the art to implement and practicethe present invention. Although the preferred embodiments of the presentinvention have been described above, those skilled in the art willappreciate that various modifications and variations can be made in thepresent invention without departing from the spirit or scope of theinvention.

INDUSTRIAL APPLICABILITY

The present invention can be applied not only to the NR system but alsoto a different wireless system in which various requirements exist.

What is claimed is:
 1. A method for transmitting demodulation referencesignals (DMRSs) for data in a wireless communication system, the methodcomprising: transmitting a basic DMRS on a first OFDM symbol within atime domain unit; and transmitting one or more additional DMRSs on oneor more second OFDM symbols located after the first OFDM symbol withinthe time domain unit; wherein a position of the first OFDM symbol isvariable based on mapping type of a data region related with a locationof starting OFDM symbol and a length of the data region, whereinpositions of the second OFDM symbols are determined based on a presenceof the first OFDM symbol, a number of the second OFDM symbols and anumber of OFDM symbols within the data region, and wherein the positionsof the second OFDM symbols are determined regardless of the variation ofthe position of the first OFDM symbol based on the mapping type of thedata region.
 2. The method of claim 1, wherein the position of the firstOFDM symbol, used for the first mapping type, is differently determinedas a second positioned OFDM symbol or a third positioned OFDM symbolwithin the time domain unit.
 3. The method of claim 1, wherein a firstpositioned OFDM symbol, among OFDM symbols assigned for the data, isdifferent from a first positioned OFDM symbol within the time domainunit.
 4. The method of claim 1, wherein the data includes a PUSCH(Physical Uplink Shared Channel) transmitted by a user equipment (UE).5. The method of claim 1, wherein the data includes a PDSCH (Physicaldownlink Shared Channel) transmitted by a network.
 6. An apparatus fortransmitting demodulation reference signals (DMRSs) for data in awireless communication system, the apparatus comprising: a transceiverconfigured to transmit a basic DMRS on a first OFDM symbol within a timedomain unit, and to transmit one or more additional DMRSs on one or moresecond OFDM symbols located after the first OFDM symbol within the timedomain unit; a processor connected to the transceiver, and configuredto: determine a variable position of the first OFDM symbol based onmapping type of a data region related with a location of starting OFDMsymbol and a length of the data region, determine positions of thesecond OFDM symbols based on a presence of the first OFDM symbol, anumber of the second OFDM symbols and a number of OFDM symbols withinthe data region, and wherein the positions of the second OFDM symbolsare determined regardless of the variable position of the first OFDMsymbol determined based on the mapping type of the data region.
 7. Theapparatus of claim 6, wherein the position of the first OFDM symbol,used for the first mapping type, is differently determined as a secondpositioned OFDM symbol or a third positioned OFDM symbol within the timedomain unit.
 8. The apparatus of claim 6, wherein a first positionedOFDM symbol, among OFDM symbols assigned for the data, is different froma first positioned OFDM symbol within the time domain unit.
 9. Theapparatus of claim 6, wherein the data includes a PUSCH (Physical UplinkShared Channel) transmitted by a user equipment (UE).
 10. The apparatusof claim 6, wherein the data includes a PDSCH (Physical downlink SharedChannel) transmitted by a network.